Generally, in a conventional digital-to-analog converter (DAC), an output voltage is required to have a linear relation with the digital data input. However, in certain special cases, an output voltage of the DAC must have a non-linear relation with the digital data input. For example, in liquid-crystal display (LCD) applications, the relation between the brightness and voltage of an LCD is not linear. Therefore, a correction circuit generally called a Gamma correction circuit which is utilized for compensation should be added into the DAC circuit. However, a conventional DAC with a Gamma correction circuit takes up so much space that it occupies most of the area of a data driver. FIG. 1 shows the structure of a R-DAC with a Gamma correction circuit according to the prior art. In this conventional R-DAC, digital data D0.about.D5 are decoded by the use of a ROM decoder 11, and then a voltage-dividing resistor 121 is selected from a reference voltage generator 12 to output a corresponding voltage. The above-mentioned approach is simple, but taking an LCD application as an example, the number of gray levels varies directly with the space occupied by its structure. For example, the area of the R-DAC with 256 gray levels is 5.3 times that of the R-DAC with 64 gray levels.
FIG. 2 is a circuit diagram of a 2-divided C-DAC with a Gamma correction circuit, including switch 13 and capacitor 14 corresponding to digital data input. Even though the area of the 2-divided C-DAC is smaller than that of the R-DAC, many capacitors which take up a large area are used. Therefore, the area of the 2-divided C-DAC can be further reduced.